Press Releases

Arena Pharmaceuticals Issued Patent for 5-HT2C Receptor Modulators by United States Patent Office

APD356, Arena's Phase 2b Small Molecule for Treatment of Obesity, Covered by Patent

Arena Pharmaceuticals Issued Patent for 5-HT2C Receptor Modulators by United States Patent Office

SAN DIEGO, Oct. 11 /PRNewswire-FirstCall/ -- Arena Pharmaceuticals, Inc.
(Nasdaq: ARNA) announced today that it was issued US patent number 6,953,787,
entitled "5-HT2C Receptor Modulators," by the United States Patent and
Trademark Office. The patent relates to novel compounds that modulate the
5-HT2C serotonin receptor, which helps regulate food intake and may also
influence metabolic rate. These modulators could be useful in pharmaceutical
compositions for the treatment of obesity. APD356, discovered by Arena, is a
selective and orally available 5-HT2C receptor modulator covered by the
patent. A 12-week, randomized, double-blind, dose-ranging Phase 2b clinical
trial studying APD356 in obese patients is currently ongoing.

"This patent, along with a similar patent granted by the European Patent
Office earlier this year, provides important protection for our lead drug
candidate, APD356," commented Jack Lief, Arena's President and Chief Executive
Officer. "We are looking forward to announcing top-line, longer term safety
and efficacy data from our Phase 2b clinical trial of APD356 around the end of
the year."

APD356 stimulates the 5-HT2C serotonin receptor, a G protein-coupled
receptor located in the part of the brain called the hypothalamus, which helps
regulate food intake and may also influence metabolic rate. APD356 has
approximately 100-fold selectivity in vitro for the 5-HT2C receptor relative
to the 5-HT2B receptor. Arena believes the 5-HT2B receptor is primarily
implicated in the cardiac valvulopathy observed with non-selective
serotonergic agents. In addition, APD356 has approximately 15-fold
selectivity in vitro for the 5-HT2C receptor versus the 5-HT2A receptor, a
central nervous system (CNS) receptor thought to be responsible for many of
the CNS adverse effects of non-selective serotonergic agents. Arena believes
that the selectivity of APD356 for the 5-HT2C receptor will allow the compound
to be dosed at a well-tolerated level that will induce clinically relevant
weight loss without the side effects observed with non-selective serotonergic
agents.

About Obesity

Obesity and a related condition known as metabolic syndrome affect tens of
millions of adults and children in the U.S. and pose a serious long-term
threat to their health and welfare. The number of overweight and obese people
has substantially increased over the past few decades. Approximately
two-thirds of all adults in the U.S. are obese or overweight and 16% of
children and adolescents ages 6 to 19 in the U.S. are overweight. Medical and
related costs of obesity in the U.S. were more than $117 billion in 2000.
Being obese or overweight is associated with a number of conditions, including
heart disease, stroke, diabetes, cancer and osteoarthritis. Medical treatment
options for obesity and metabolic syndrome are currently limited.

About Arena Pharmaceuticals

Arena is a clinical-stage biopharmaceutical company focusing on the
discovery, development and commercialization of small molecule drugs in four
major therapeutic areas: metabolic, cardiovascular, inflammatory and central
nervous system diseases. Arena is developing a broad pipeline of compounds
that act on an important class of drug targets called G protein-coupled
receptors, or GPCRs, using its knowledge of GPCRs and its technologies,
including CART (Constitutively Activated Receptor Technology) and
Melanophore. Arena has three internally discovered, clinical-stage product
candidates. Arena's most advanced clinical compound, APD356, a selective
5-HT2C serotonin receptor agonist for the treatment of obesity, is in Phase
2b. Arena's lead product candidate for the treatment of insomnia, APD125, a
compound with a novel mechanism of action (a selective 5-HT2A receptor inverse
agonist), is scheduled to begin a Phase 2 clinical trial by the end of 2005.
As part of Arena's partnership with Merck & Co., Inc., an Arena product
candidate for the treatment of atherosclerosis and related disorders is in a
Phase 1 clinical trial. Arena also has an active collaboration with
Ortho-McNeil, Inc., a Johnson & Johnson company, for the treatment of type 2
diabetes.

Arena Pharmaceuticals® and Arena® are registered service marks of the
company. CART is an unregistered service mark of the company.

Forward-Looking Statements

Certain statements in this press release are forward-looking statements
that involve a number of risks and uncertainties. Such forward-looking
statements include statements about the possible usefulness of 5-HT2C
modulators in pharmaceutical compositions for the treatment of obesity,
APD356's safety profile, potency and pharmaceutical behavior, the significance
of, and the protection provided by APD356 patents, and the expected timing of
Arena's clinical trials and announcement of results and other statements about
Arena's strategy, technologies, preclinical and clinical programs, and ability
to develop compounds and commercialize drugs. For such statements, Arena
claims the protection of the Private Securities Litigation Reform Act of 1995.
Actual events or results may differ materially from Arena's expectations.
Factors that could cause actual results to differ materially from the
forward-looking statements include, but are not limited to, the results of
Arena's clinical trials, the results of preclinical studies or clinical trials
may not be predictive of future results, Arena's ability to partner APD356,
APD125 or other of its compounds or programs, the timing, success and cost of
Arena's research, out-licensing endeavors and clinical trials, Arena's ability
to obtain additional financing, Arena's ability to obtain and defend its
patents, Arena's patent protection, and the timing and receipt of payments and
fees, if any, from Arena's collaborators, including Ortho-McNeil and Merck.
Additional factors that could cause actual results to differ materially from
those stated or implied by Arena's forward-looking statements are disclosed in
Arena's filings with the Securities and Exchange Commission. These
forward-looking statements represent Arena's judgment as of the time of this
release. Arena disclaims any intent or obligation to update these forward-
looking statements, other than as may be required under applicable law.